The present invention relates to a device for pivoting at least one pivotable element in a gas turbine engine between a first and a second position in order to influence a gas flow in an annular gas duct in at least one of said positions, the device comprising a moveable annular member, which is arranged externally around the gas duct and is connected to the pivotable element in order to effect the pivoting of the pivotable element. The invention also relates to a gas turbine engine comprising the device.
The device can be used in order to regulate the tapping (bleeding) of air. The device will be described below for opening and closing an opening in a wall, which defines a gas duct for bleeding air. Multiple bleed openings are conventionally spaced at intervals from one another in a circumferential direction around the gas duct and through the gas duct wall. A corresponding number of pivotable elements are correspondingly spaced at intervals from one another in a circumferential direction and form doors, or hatches, designed to control the degree of opening of the openings.
The device will be described for a jet engine in an aircraft. In known aircraft engines a bleed line extends between a primary gas duct and a secondary gas duct for bleeding off air from the primary gas duct to the secondary gas duct. In certain operating situations compressed air is bled off from the primary gas duct via the bleed line and is introduced into a high-velocity flow in the secondary gas duct.
The term jet engine is intended to encompass different types of engines which draw in air at relatively low velocity, heat this up by through combustion, and expel it at a much higher velocity. The term jet engine includes turbojet engines and turbofan engines, for example. The invention will be described below for a turbofan engine, but can obviously also be used for other types of engines.
U.S. Pat. No. 6,742,324 shows a valve system for the variable control of a gas bypass. The system comprises a unison ring, which is arranged radially outside a gas duct wall. The ring is connected to a bypass hatch, which covers an opening through the wall via a bell-crank lever. The ring is arranged to pivot in a circumferential direction and the hatch is opened and closed when the ring is pivoted in its circumferential direction.
It is desirable to provide a device for pivoting at least one pivotable element in a gas turbine engine, especially a bleed hatch, which represents an alternative to known solutions. It is also desirable to achieve a longer service life than such devices hitherto known.
According to an aspect of the present invention, the annular member is arranged to be displaced in a substantially axial direction and is arranged to pivot the pivotable element when it is displaced axially.
Such an axial, straight movement creates the prerequisites for a more reliable functioning in operation. Furthermore, fewer friction losses occur. In addition, the device is less sensitive to problems associated with the different rates of expansion of the constituent components, which can occur owing to thermal loads.
According to a preferred embodiment of the invention the pivotable element forms a hatch, which is arranged to open and close an opening in a wall, which defines the gas duct for the purpose of bleeding gas. In this case the pivotable element influences the gas flow when it is disposed in a open position, whereas the gas flow passes the pivotable element unaffected when the pivotable element is in a closed position. Multiple doors are preferably arranged at intervals from one another in a circumferential direction and each door is positioned in order to open and close one opening in the wall.
According to another preferred embodiment of the invention the pivotable element forms a guide vane which is arranged in the gas duct, the guide vane being arranged to be positioned in at least two different angular positions. Multiple guide vanes are preferably spaced at intervals from one another in a circumferential direction. The guide vanes are arranged in a fixed part of the gas turbine and the gas flow passes the guide vanes in the space between these. In this case the guide vanes influence the passing gas flow to a different extent depending on their angular setting.
According to a further preferred embodiment of the invention, the device comprises at least one motion-transmitting member, which mechanically connects the axially displaceable annular member and the pivotable element. An axial displacement of the annular member will thereby be transmitted to the pivotable element via an at least substantially axial displacement of the motion-transmitting member, which creates the prerequisites for reliable functioning in operation.
According to a further preferred embodiment of the invention, the device comprises a linkage mechanism, which supports the axially displaceable annular member in relation to a fixed part and is arranged to control the axial movement of the annular member.
According to a more detailed design of the last aforementioned embodiment, the linkage mechanism comprises at least two parallel stabilizer bars, a first stabilizer bar being pivotably connected to the annular member at two separate positions in a circumferential direction, and a second stabilizer bar being pivotably connected to the fixed part at two separate positions in a circumferential direction. The stabilizer bars mean that the movement can be controlled so that all pivotable elements are pivoted in the same way and equally far.
Further advantageous embodiments and further advantages of the invention are set forth in the detailed description below, in the drawings.